The present invention relates to a multiplex communication system and a car-passenger protection system using the same. Conventionally, a multiplex communication system as shown in FIG. 1 is known. Specifically, a master unit 100 includes a microcomputer 101 and an acceleration sensor. The master unit 100 is coupled to a plurality of satellite units 103A, 103B, . . . , and 103N via a reference bus 102, and coupled to the plurality of satellite units 103A, 103B, . . . , and 103N via a signal transmission bus 104. Squibs 105A, . . . , and 105N are coupled to the satellite units 103A, 103B, . . . , and 103N, respectively.
The satellite units 103A to 103N are located on the side portion of a car such as a door panel apart from the master unit 100 positioned at the center of the car. Signals are respectively supplied to the satellite units 103A to 103N through the signal transmission bus 104 from the master units 100. Electric energy is supplied to each of the satellite units 103A to 103N by voltage multiplexing. A part of the electric energy transmitted to each of the satellite units 103A to 103N is used for allowing the satellite unit 103A to 103N to operate. Other parts are stored in the satellite unit 103A, and the electric energy stored in the satellite unit 103A is supplied to the squib 105A as ignition current when an airbag needs to be developed at the time of an accident. There is a technology disclosed in Japanese Patent Laid-Open No. 10(1998)-154992 as such a kind of prior art.